The present invention relates generally to laminated parts for use in electric motors and generators. More particularly, the present invention relates to electric motor or generator stators and rotors having stacked laminae and the methods and machines, i.e., progressive dies and controllers therefor, used in the manufacture of such laminated parts.
The manufacture of stators and rotors employing stacked laminae is well known in the art. Typically, the laminae are blanked from continuous strip stock and then stacked and bound together to form the stator or rotor. Progressive die assemblies for producing stator or rotor laminations wherein a strip of lamination material is fed through a sequence of punching steps to progressively form the laminae are also well known.
Rotor laminae generally include a plurality of skewed conductor slots which are formed around the periphery of the rotor stack in arcuately spaced relation to one another by rotationally indexing the laminae with respect to the rotor stack axis. Indexing involves rotating the rotor stack and the last produced lamina relative to each other by a predetermined rotational increment so that, when the laminae are combined in a stack, the rotor conductor bar slots defined by adjacent conductor slots are skewed or slanted relative to the stack axis. Stator stacks, on the other hand, include winding slots around the inner periphery of the stack which extend parallel to the stack axis, without skew, and are shaped to receive the stator windings. Although relatively rare, inside-out motors are often used in fan motor designs and utilize inner cores manufactured with straight slots to be used with outer cores having skewed slots, in which case it would be the outer core laminations which are rotated relative to each other to produce the skew angle.
In addition to producing a skew angle, as discussed above, the relative rotation of a lamina and the lamina stack onto which the lamina will be placed can be used to overcome the negative effects created by thickness inconsistencies in the strip stock from which the laminae are blanked. The strip stock used to manufacture lamina stacks may have thickness inconsistencies wherein one side of the strip stock is thicker than the other side. If laminae punched from the strip stock are stacked without rotation, the lamination stack produced will not have a uniform height around its entire perimeter because the stacking of the individual laminae will additively compound the thickness inconsistencies present in the strip stock on one side of the stack. A stack having a substantially uniform height can be produced, however, by rotating individual laminae relative to the lamina stack to equally distribute the thickness inconsistencies about the stack axis. The inconsistencies thereby cancel each other out in a known process often referred to as gamma correction.
In response to these problems, an autorotation system to compensate for nonuniform stock thickness was developed which both rotates and interlocks the stacked laminae. This system compensates for variations in lamina thickness while properly skewing the conductor slots of rotor laminae, as described in U.S. Pat. Nos. 4,619,028; 4,738,020; 5,087,849 and 5,123,155, all assigned to the assignee of the present invention and the disclosures of which are expressly incorporated herein by reference. In the systems disclosed in the aforementioned patents, the choke barrel holding the lamination stack is automatically rotated before each lamina is blanked from the strip stock and the lamina""s circumferentially disposed tabs are interlocked with the slots of the uppermost lamina of the incomplete lamination stack within the barrel.
In the apparatus and method disclosed in the aforementioned patents, the individual laminae are typically rotated through an angle which is the sum of 180xc2x0 to provide for gamma correction plus a smaller incremental amount necessary to provide the proper skew angle. Although the laminae may be rotated through other angles, the angle, without including the incremental rotation necessary to produce the skew angle, must be at least 360xc2x0/(number of interlock tabs) to permit the use of interlocking tabs and slots.
The use of an AC or DC servomotor and a controller allows the operator of the die assembly to rapidly and easily alter the rotational amounts to produce different skew angles or to alter the angle through which the laminae are rotated to correct for thickness inconsistencies. The controller computes a single angle through which the choke barrel must be rotated to provide for both gamma correction and a proper skew angle. The use of a servometor to rotate a choke barrel for such purposes, however, places a limit on the number of strokes per minute of the die assembly because it requires the use of a relatively large, and relatively slow, servo drive unit which has the capacity to handle the inertial loads involved in rotating the choke barrel through such large angles between each stroke of the die assembly as well as to be sufficiently accurate. Typical achievable rates are 275 to 300 strokes/minute. Notably, the life of the servomotor in such a system is not particularly long; in addition to providing the desired skew angle, the motor must also provide the necessary gamma correction. A faster indexing system, which also extends servomotor life, is desirable.
Mechanical indexers which utilize a camming assembly such as a roller cam to provide indexed rotational movements to rotate the choke barrel are also known and may be used to provide for gamma correction while allowing the die assembly to operate at significantly higher rates, e.g., in the range of 400 to 500 strokes/minute, than a comparable servo drive assembly. Indexers of the type used for rotating choke barrels in stamping die apparatuses are manufactured by the Ferguson Company, 11820 Lackland Road, St. Louis, Mo. 67146. Mechanical indexers used for gamma correction lack the flexibility of servo drive systems, however, since the angle at which they rotate the choke barrel cannot be easily adjusted.
A mechanical system has also been developed to provide for the incremental indexing of laminae to provide a proper skew angle and U.S. Pat. No. 3,203,077 provides one example. Although such a mechanical system provides for some adjustment of the amount of rotational indexing necessary for a skew angle, the adjustment of mechanical indexing systems is not as flexible or convenient as the adjustment of a servo drive motor which is regulated by a controller.
A system which utilizes a modified roller cam assembly to provide a mechanical indexer in conjunction with a system for providing an incremental rotational movement for producing a skew angle is disclosed by U.S. Pat. No. 5,163,217. The disclosed system, however, cannot employ a standard xe2x80x9coff the shelfxe2x80x9d roller cam assembly thereby increasing the cost of the system. The disclosed system also employs a plurality of small rollers which are in frictional contact between an input roller and an output disk. The use of such frictionally engaged surfaces to transmit rotational movements is more subject to slippage than an arrangement involving the transfer of rotational movement by positively locking gear teeth.
A system which utilizes a differential device having an output shaft which is coupled to the rotary choke barrel of a die stamping apparatus, an input shaft which is driven by a mechanical indexer to impart gamma correction with each press cycle, and a housing or casing incrementally rotated by a servomotor to impart a fixed amount of skew angle with each press cycle, is disclosed in U.S. Pat. No. 4,615,207. The differential device thus serves as a phase adjuster which combines the gamma correction and the skew angle. A rotary cam switch is attached to the press crank and, with each cycle of the press, provides a timing signal to a control circuit which actuates the servomotor, causing it to rotate through a small, fixed angle. The output shaft of the servomotor is provided with a worm gear which is enmeshed with a ring gear provided on the rotatable differential housing or casing. Thus, in addition to being rotated through the index angle (e.g., 180xc2x0) for gamma correction by the input shaft and internal gearing of the differential device, the out put shaft of the differential device is additionally rotated through the skew angle, via rotation of the differential casing by the servomotor through the worm gearing.
Worm gearing is used for obtaining large speed reductions between nonintersecting shafts making an angle of 90xc2x0 with each other. Generally, the lead angle of the helical worm gear thread is rather shallow, and the surfaces along which the worm gear and ring gear interface lie substantially in planes which are almost normal to the longitudinal axis of the worm gear; i.e., a plane normal to the worm gear axis would form a very small angle relative to the planes in which the worm gear and ring gear interfaces lie. In any given angular ring gear position, a tooth of the ring gear is captured between adjacent worm gear thread portions, linearly in the direction of the worm gear""s longitudinal axis. The direct mechanical link between a worm gear thread and a ring gear tooth counteracts and absorbs the inertial forces exerted by the choke barrel at the beginning and end of each indexing cycle.
It is typical in worm gearing applications that rotation of the (driving) worm gear by the intermeshed (driven) ring gear is prevented by the nearly normal angle of their interface relative to the worm gear""s axis of rotation. Thus, in phase adjusters utilizing a worm gear/ring gear arrangement for imparting a skew angle, it is the interface between the worm and ring gears which holds the position of the differential casing, and thus absorbs the reversing inertial loads imparted by the rotating choke barrel and differential.
A problem encountered with differential type phase adjusters of the type disclosed in U.S. Pat. No. 4,615,207, stems from the worm gear/ring gear interface being subjected to the reversing inertial load imparted thereon by the rotating choke barrel. This problem is particularly severe at high indexing rotation frequencies (e.g., 400 to 500 times per minute) and may lead to premature failure of the phase adjuster.
For example, a Model DIFF30 differential unit produced by the Candy Manufacturing Company of Niles, Ill., of the type disclosed in U.S. Pat. No. 4,615,207, was used as the phase adjuster in a die assembly and subjected to reversing inertial loads by the rotating choke barrel at a rate of 400 to 500 times per minute. That differential unit failed completely within about 20 minutes. Thus, at these press cycle rates, the projected life of this unit is only about 8000 to 10,000 press cycles, and it would likely be practically inoperable long before due to unacceptable backlash between the worm gear and ring gear.
A Model B-50ZMV-10 differential unit, manufactured by Wedgetrac Corporation of Rockford, Ill., is of zero velocity gear mesh type disclosed in U.S. Pat. No. 5,613,919, the disclosure of which is expressly incorporated herein by reference. This differential unit also uses a worm gear/ring gear arrangement, and was substituted for the above Candy Model DIFF30 differential unit. Although the Wedgetrac Model B-50ZMV-10 differential unit lasted approximately 20 hours (i.e., approximately 480,000 to 600,000 press cycles at normal operating speeds) before a backlash problem between its worm gear and ring gear developed, and thus proved substantially more durable than the Model DIFF30 unit, an even more durable means for combining the gamma correction and skew angle is needed to accommodate press cycle rates of 400 to 500 per minute in a die assembly apparatus of the type described hereinbelow.
It appears that the direct interface between the worm gear and the ring gear is the weak link in previous phase adjusters. With respect to the failed Model DIFF30 and Model B-50ZMV-10 differential units described above, it is believed that, because the substantial, reversing inertia forces associated with quickly starting and stopping the choke barrel and differential device are exerted on and between the abutting, mating worm and worm gear surfaces at angles which are almost normal to those surfaces, the worm and worm gear cannot accommodate the repeated inertial shocks delivered through the differential casing by the rotating choke. Rather than being glanced along the worm and/or worm gear tooth surfaces, the entirety of these forces are imposed thereon at angles which are nearly normal thereto, and must be directly absorbed by the worm/worm gear interface. As indexing is initiated, the inertial load of the choke barrel and differential device is imparted first on one pair of interfacing worm thread portion/worm gear tooth surfaces, located on one side of the worm gear tooth; as indexing is completed, the inertial load reverses, and is imparted on another pair of interfacing worm thread portion/worm gear tooth surfaces, located on the opposite side of that worm gear tooth.
Notably, at an operating speed of 400 press cycles per minute, over the course of a month, a die stamping apparatus may cycle well over 6.5 million times. From the above discussion, it should be apparent that phase adjusters having worm gearing arrangements may be inadequate for achieving such high production rates. A phase adjuster which overcomes the above-described weaknesses of phase adjusters having worm gearing arrangements, and which quickly and accurately combines gamma correction and skew angle, is thus desirable.
Further, although it may be possible to employ a more robust differential unit having a worm gear/ring gear link to a servomotor which is durable enough to provide a satisfactory life expectancy, the mass of, and frictional losses within, such differentials are. expected to be quite high. Therefore a substantially greater amount of energy would be required to drive such an indexing unit. This additional energy would be drawn from the press crank, and would then not be available for powering the stamping operations of the die apparatus. Moreover, it is expected that a differential unit sufficiently large enough to prevent premature failure at the worm gear/ring gear interface would have an inertia too large to accommodate cycle speeds anywhere near 400 to 500 per minute. Therefore, a smaller, lighter differential unit is much preferred.
The present invention provides a lamination indexing system which relatively rotates individual laminations with respect to a stack of laminations using both a mechanical indexer having a conventional roller cam assembly and a servo drive unit. By using a mechanical indexer to provide the larger rotational angle necessary to correct for thickness inconsistencies, a small, fast, and accurate servo drive motor can be used to provide the rotational indexing necessary to obtain the proper skew angle. The combination of these two rotation systems is made possible by using a phase adjuster which permits the combination of the two separate rotational outputs provided by the respective systems. In particular, the phase adjuster for use in combining the two separate rotational outputs provided by the respective systems is a zero velocity gear mesh differential or a step-up ratio differential.
An advantage of the present invention is that a lamina and a lamina stack may be relatively rotated in the approximate range of 400 to 500 cycles/minute to provide for both gamma correction and the incremental indexing necessary to provide a desired skew angle which is much faster than a system employing only a large servo drive motor. The increased rate of operation is made possible because both the mechanical indexer and the small servo drive motor are faster than a large servo drive motor and the phase adjuster allows the mechanical indexer and small servo drive motor to simultaneously rotate the choke barrel.
Another advantage of the present invention is that it permits operation of the die assembly at higher rates than those obtainable with a die assembly having a large servomotor in isolation while still providing the ability to properly index the laminae to produce a desired skew angle.
Yet another advantage of the present invention is that it permits operation of the die assembly at higher rates than those obtainable with a die assembly having a large servomotor while still providing the ability to rapidly and conveniently alter the skew angle.
A still further advantage of the present invention is that the use of a zero velocity gear mesh differential provides a rugged indexing system with a long life, and also extends the life of the servomotor vis-a-vis prior indexing systems which rely on the servomotor to provide both the skew angle and gamma correction. In accordance with the present invention, the amount of work performed by the servomotor is comparatively reduced by a substantial amount, thereby extending the life of the motor.
Furthermore, the present invention provides an indexing system for a die assembly for manufacturing a stack of laminae from sheet stock material in a punch press, the stack having a desired stack height and a skew angle, the stock material having a nominal thickness. The indexing system includes indexing means for producing a first indexing input movement in response to movement of the punch press, a motor for producing a second indexing input movement in response to a control signal, and differential means for combining the first and second indexing input movements into an indexing output movement and having first and second input means for respectively receiving the first and second indexing input movements. The first input means is coupled to the indexing means, and the second input means is coupled to the motor. The differential means also has output means for transmitting the indexing output movement; a rotatable choke barrel in which laminae are received and stacked. The choke barrel is rotationally coupled to the output means, and is rotated in accordance with the indexing output movement. Cyclical inertial loads imparted by the choke barrel are absorbed within the motor.
Thus, an even more durable phase adjuster is provided which overcomes the weaknesses of some prior indexing systems which employ worm gearing to hold the choke barrel at the desired punching orientation and impart the phase angle thereto. This embodiment of the present invention does not rely on worm gearing to impart the skew angle, or to absorb the reversing inertial load imparted by the rotating choke barrel. According to this embodiment of the present invention, the reversing inertial loads imparted by the rotating choke barrel are absorbed by the motor. One example of this embodiment of the present invention has an anticipated life of approximately 20,000 hours. At 400 press cycles per minute, this life is estimated at approximately 480 million cycles. At 6.5 million cycles per month at 400 press cycles per minute, it is estimated that this particular embodiment of the present invention will be greater than six years.
The present invention also provides an indexing system for a die assembly for manufacturing a stack of laminae from sheet stock material in a punch press, the stack having a desired stack height and a skew angle, the stock material having a nominal thickness. The inventive indexing system includes an indexer including a rotatable output member having a movement which corresponds to movement of the punch press, a motor including a rotatable output member having a movement which is made in response to a control signal, and a differential having first and second rotatable input members and a rotatable output member, the rotational movement of the differential first and second rotatable input members being combined by the differential into the rotational movement of the differential output member. The indexer output member is coupled to the differential first input member, and the motor output member being coupled to the differential second input member. The inventive indexing system includes a rotatable choke barrel in which laminae are received and stacked, the choke barrel being rotatably coupled to the differential rotatable output member, whereby rotation of the differential output member causes the choke barrel to rotate, and wherein inertial loading by the choke barrel on the differential second input member is transmitted to, and absorbed by, the motor.
Further, the present invention also provides a method of indexing a rotatable choke barrel, in which laminae punched from sheet stock material are received and stacked, with a differential having rotatable first and second input members and a rotatable output member which is coupled to the choke barrel, whereby the choke barrel is rotated by the differential output member. The inventive methods includes: rotating the differential first input member through a first angle; rotating the differential second input member through a second angle; combining the rotations of the differential first and second input members into a rotation of the differential output member through a third angle; rotating the choke barrel between first and second angular positions; and resiliently absorbing at least a portion of the rotational inertia of the choke barrel imparted on the differential as the choke barrel respectively leaves and reaches its first and second angular positions.